The conventional method of producing hardfaced plate, as described in my U.S. Pat. No. 3,494,749, with bulk welding as described in that Patent and my U.S. Pat. Nos. 3,076,888 and 3,060,307 has been to strap down a plate and try to hold it from distorting while making the weld deposits with one or two beads along the length of the plate. When the deposit is made on 1/2" or thicker plate, the plate remains reasonably flat and the deposit can be made in a reasonably uniform manner. However, the great majority of this hardfaced plate is used in the 1/4" and 3/8" sizes since much of it is used in fan blades where weight is a major problem. When these thicknesses are clad in the flat position, the heat of welding combined with the shrinkage of the weld coating on cooling causes a buckling of the plate with undesirable effects that affect the quality of the deposit, and in most cases, the ability to clad the plate with more than one bead at a time.
When the plate buckles toward the weld nozzle, the distance from the weld zone on the plate to the welding nozzle is changed as illustrated in FIG. 1. The buckle is such that the distance of the welding wire (called "stickout") is decreased which calls for a greater amount of current in the weld operation to melt the welding wire since it must be heated from ambient to melting, while the wire is traveling a relatively short distance from the welding nozzle to the weld zone. This greater current will cause undesirable penetration into the plate and dilute the overlay with iron from the plate.
If the buckle is away from the nozzle as illustrated in FIG. 2, the welding operation requires less current because the longer distance which the welding wire travels from the welding nozzle to the work causes it to heat to melting with less rate of heat input because of the longer time of heating. This lower than normal current will result in insufficient melting of the base plate and loss of bond for the facing and will often cause incomplete melting of the granular hardfacing materials resulting in a "lean" alloy.
In addition, the buckling causes the plate to be unlevel and the deposit applied will tend to flow away from the weld zone and form a non-uniform, non-level overlay layer of too-heavy or too-light thickness.
The use of multiple welding heads serves to compound the problem and results in limiting the number of weld heads to one or two depending on the thickness of the plate to be clad. Also, in the cladding of thinner plate, such as 1/4", the plate heats through and tends to melt too easily in the weld zone giving unwanted dilution of the deposit with iron from the plate.
Additionally, the flat plate method gives a low percentage of total welding time in the cladding or hardfacing operation because after welding only one or two beads the length of the plate, the operation must be stopped, the weld bead or beads cleaned and the plate or the heads returned to the starting end and repositioned before the welding can again be started. The total time to clad a plate is thus increased by between 50 and 100%, depending on the efficiency of cleaning, returning to start, and repositioning the weld heads depositing the beads.
It would be highly advantageous to provide methods of overlaying or hardfacing plate which eliminate all of the foregoing difficulties.